Production of well-matured compost from night-soil sludge by an extremely short period of thermophilic composting

Abstract The effect of various operational conditions on the decomposition of organic material during the composting of night-soil treatment sludge was quantitatively examined. The optimum composting conditions were found to be a temperature of ca. 60 °C and an initial pH value of 8. Rapid decomposition of organic matter ceased by the sixth day of composting under these optimum conditions, and the final value of the cumulative emission of carbon ( E C ), which represents the degree of organic matter decomposition, was less than 40%, indicating that the sludge contained only a small amount of easily degradable organic material. A plant growth assay using Komatsuna ( Brassica campestris L. var. rapiferafroug ) in a 1/5000a standard cultivation pot was then conducted for the compost at various degrees of organic matter decomposition: the raw composting material, the final compost obtained on day 6, and the 2 intermediate compost products (i.e., E C  = 10% and 20%). It was found that the larger the E C , the greater the yield of Komatsuna growth. It was also found that 6 days of composting is sufficient to promote Komatsuna growth at the standard loading level, which is equivalent to a 1.5 g N/pot, since the promotion effect was as high as that obtained using chemical fertilizer. It can therefore be concluded that well-matured compost could be obtained in a short period of time (i.e., as early as 6 days), when night-soil sludge is composted under optimum conditions.